Feature Request: schemadiff to calculate "Row size too large" and index size

[shlomi-noach]

Feature Description

MySQL/InnoDB limit the total size of char and binary columns:

• 8126 for COMPACT
• 65535 for DYNAMIC, COMPRESSED

Key length is limited to:

• 767 bytes for COMPACT,
• 3072 bytes for DYNAMIC, COMPRESSED

These lengths depend on the character set used for char columns. schemadiff's validate() function should be able to compute these.

Use Case(s)

Better schema validation by schemadiff.

[shlomi-noach]

Simple table structure to test with:

CREATE TABLE `t` (
	`id` int NOT NULL AUTO_INCREMENT,
	`v1` varchar(1000) NOT NULL,
	`v2` varchar(1000) NOT NULL,
	`v3` varchar(1000) NOT NULL,
	`v4` varchar(1000) NOT NULL,
	`v5` varchar(1000) NOT NULL,
	`v6` varchar(1000) NOT NULL,
	`v7` varchar(1000) NOT NULL,
	PRIMARY KEY (`id`),
	KEY `v1_idx` (`v1`)
) ENGINE InnoDB,
  CHARSET utf8mb3,
  ROW_FORMAT COMPACT;

[shlomi-noach]

InnoDB snippet:

uint ha_innobase::max_supported_key_part_length(
    HA_CREATE_INFO *create_info) const {
  /* A table format specific index column length check will be performed
  at ha_innobase::add_index() and row_create_index_for_mysql() */
  switch (create_info->row_type) {
    case ROW_TYPE_REDUNDANT:
    case ROW_TYPE_COMPACT:
      return (REC_ANTELOPE_MAX_INDEX_COL_LEN - 1);
      break;
    default:
      return (REC_VERSION_56_MAX_INDEX_COL_LEN);
  }
}